Reproductive tract infections (RTI) are of particular relevance during pregnancy and have important implications for maternal and neonatal health. Both bacterial vaginosis and group B Streptococcus are RTI associated with biofilm formation and long-term colonization of the vaginal mucosal surface. We have found that both Gardnerella vaginalis (the major constituent of the vaginal microbiota during bacterial vaginosis) and group B Streptococcus (the leading cause of early-onset sepsis in newborns) form biofilms that contain extracellular DNA and are sensitive to the activity of exogenous DNase. Thus, we hypothesize that an intravaginal DNase gel could decrease the risk of these and potentially other RTI in late pregnancy. Our overall goal is to rigorously evaluate this hypothesis by formulating a lead candidate DNase gel for in vitro and in vivo testing and by leveraging our experience in microbicide acceptability studies to determine potential barriers to the real-world use of such a preventive strategy during pregnancy. In the proposed sequential R21/R33 phased innovation study, the R21 phase will focus on formulation of DNase gel prototypes and evaluation of efficacy against RTI relevant to pregnancy using in vitro and in vivo models and on developing behavioral instruments to study microbicide acceptability in pregnant women. In the R33 phase, we will optimize the lead gel candidate, perform expanded efficacy and toxicology studies in vivo, and use our behavioral instrument to study locally and nationally representative populations of pregnant women. At the conclusion of the two phases, we will have completed a detailed preclinical evaluation of a DNase gel for the prevention of two important RTI in pregnancy and will have performed an assessment of behavioral factors important to the implementation of such a strategy. If a suitable gel advances to the conclusion of the R33 phase with in vivo efficacy and an acceptable toxicologic profile, we will move forward with the eventual goal of human testing.